The measurement methods of chromatograph mass spectrometers such as the GC/MS or LC/MS can be classified into two modes, i.e. the scan measurement and the selected ion monitoring (SIM) measurement. In the scan measurement mode, the mass spectrometer scans the mass-to-charge ratios (m/z) of ions to be analyzed over a predetermined mass range in order to detect all varieties of ions included in the aforementioned mass range. This mode of measurement is particularly useful in the case where the mass-to-charge ratio of the component of interest is unknown, as in the case of a qualitative analysis of an unknown sample. However, this mode is not suitable for quantitative analyses since the signal-to-noise (S/N) ratio of the resultant mass chromatogram is rather low. On the other hand, in the SIM measurement mode, one or more ions with previously-specified mass-to-charge ratios are selectively detected in a time-sharing manner. This mode of measurement is useful in the case where the quantity of a known kind of substance should be measured with high sensitivity. However, this mode is not suitable for qualitative analyses since it detects only the ions having specific mass-to-charge ratios.
As explained previously, the scan measurement and the SIM measurement are complementary to each other. To utilize the characteristics of these methods, a simultaneous scan/SIM measurement method has been proposed (for example, refer to Patent Document 1), in which the scan measurement and the SIM measurement are simultaneously performed in a specified time range. This method is capable of simultaneously producing both a mass spectrum for a qualitative mass analysis and a chromatogram with a high S/N ratio for a quantitative analysis of a target ion, by one cycle of analyzing operations.
Although the simultaneous scan/SIM measurement method is a useful technique, the method causes the problem that, if this mode of measurement is performed on a large number of compounds including the compounds that do not actually need to undergo the simultaneous scan/SIM measurement, then there will be too large an amount of ions introduced into the detector per unit time, which deteriorates the detection sensitivity. Accordingly, it is often the case that the simultaneous scan/SIM measurement is only performed on the compounds for which a mass spectrum with an adequately high S/N ratio cannot be created by the normal scan measurement, whereas only the scan measurement is performed on the other compounds. Therefore, in advance of the measurement, it is necessary to select target compounds that should undergo the simultaneous scan/SIM measurement, and to specify mass-to-charge ratios at which the measurement should be performed.
In the case of a conventional chromatograph mass spectrometer, this measurement is typically performed as follows. First, with the apparatus in the scan mode, an operator performs a preliminary measurement of a standard sample containing known components to obtain a chromatogram (total ion chromatogram) of the sample. This chromatogram is used to determine whether or not each of the target compounds (i.e. the compounds to be quantitatively measured) can be detected with an adequately high S/N ratio. Based on the determination results, the operator selects target compounds that should be subjected to the simultaneous scan/SIM measurement. Subsequently, the operator specifies the time range for the simultaneous scan/SIM measurement and the mass-to-charge ratios at which the SIM measurement should be performed within the time range so that the peaks of the selected target compounds will be covered by the measurement.
Subsequently, the operator performs a predetermined operation on an input unit of the apparatus to display a measurement condition table, as shown in FIG. 7. In this table, the operator enters, for each measurement time range, the start time, finish time, measurement mode (scan or SIM), mass range (i.e. the starting and finishing values of m/z) for the scan measurement or mass-to-charge ratios for the SIM measurement, and other numerical values. After the necessary items of information are completely set, the operator fixes the settings. According to the measurement conditions thus specified, the apparatus performs the measurement of a standard sample for calibration and then the measurement of an unknown sample.
In the example of FIG. 7(a), a scan measurement is performed over a mass range from 100 to 400 for a period of time from 6 to 20 minutes in terms of the time elapsed from the measurement start time (zero minutes). On the other hand, in the example of FIG. 7(b), a scan measurement is initially performed over a mass range from 100 to 400 for a period of time from 6 to 11 minutes in terms of the time elapsed from the measurement start time (the first row of the table). Next, from 11 to 13 minutes, the scan measurement is performed over the mass range from 100 to 400 (the second row of the table), with which an SIM measurement is simultaneously carried out at four mass-to-charge ratios of 100, 200, 300 and 400 (the third row of the table). Finally, from 13 to 20 minutes, the scan measurement is performed over the mass range from 100 to 400 (the fourth row of the table).
In the example of FIG. 7(b), the simultaneous scan/SIM measurement is only performed on one compound. However, in actual analyses, the sample may contain more than 100 components, in which case the number of compounds to be measured in the simultaneous scan/SIM mode accordingly increases. Starting from a simple table, like the one in FIG. 7(a) in which conditional information for a scan measurement is set for a specific measurement time range (6 to 20 minutes in the present example), if conditions for the simultaneous scan/SIM measurement of a new target compound must be added as shown in FIG. 7(b), it is necessary for the operator to add three rows to the measurement condition table and perform key operations to enter parametric values into the cells of each of the three rows. If ten components are to be added for the simultaneous scan/SIM measurement, it is necessary to add up to 30 rows to the measurement condition table and enter necessary information into these rows. Thus, if there are many components, this task will be extremely troublesome for the operator and potentially cause more input errors.
Another problem relates to the setting of a time range for the simultaneous scan/SIM measurement. The operator has to correctly set this time range when inputting numerical values into the measurement condition table. For example, suppose that a chromatogram has two components represented by two peaks whose retention times are close to each other, and a boundary of the time range for the simultaneous scan/SIM measurement is set between these two peaks. Then, the two peaks inevitably exist in the vicinity of the boundary. In this case, even a small shift of the retention time during the measurement of an unknown sample causes one peak of the chromatogram to overlap this boundary of the time range. This situation leads to an incorrect detection of the peak and wrong calculation of the peak area, so that the quantitative analysis cannot be correctly performed. To avoid this problem, it is necessary to carefully set the time range for the simultaneous scan/SIM measurement, referring to the chromatogram obtained by the preliminary measurement of a standard sample. However, in the case of conventional apparatuses, it is difficult to precisely perform this setting since the apparatuses have no means for referring to the preliminarily obtained chromatogram on the same screen when setting the time range for the simultaneous scan/SIM measurement as described earlier.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H08-102282